Conventionally, a shaft seal mechanism for reducing a leakage of a fluid from a high pressure side to a low pressure side is disposed in the vicinity of a rotating shaft of a steam turbine or a gas turbine, in order to suppress a loss of driving force. Such a shaft seal mechanism has a ring-shaped seal structure in which thin-plate seal pieces having flat plate shapes with their width dimensions being in the rotating shaft direction are arranged into multiple layers in the circumferential direction of the rotating shaft. Outer-circumferential-side proximal end sections of the thin-plate seal pieces are fixed to a ring-shaped seal housing; on the other hand, inner-circumferential-side distal end sections of the thin-plate seal pieces are in sliding contact with the outer circumferential surface of the rotating shaft at a predetermined preload. In the shaft seal mechanism having this configuration, the surrounding space of the rotating shaft can be divided into a high-pressure-side region and a low-pressure-side region with the boundary formed by a large number of the thin-plate seal pieces arranged into a ring shape outward in the radial direction of the rotating shaft.
While the rotation of the rotating shaft is stopping, the inner-circumferential-side distal end sections of the thin-plate seal pieces are into contact with the outer circumferential surface of the rotating shaft at the predetermined preload. On the other hand, while the rotating shaft is rotating, the thin-plate seal pieces are bent by pressure difference due to relative positional shift in pressure distribution between the top and bottom surfaces of the thin-plate seal pieces and by dynamic pressure effect of the fluid generated by the rotation of the rotating shaft, and accordingly, the inner-circumferential-side distal end sections of the thin-plate seal pieces are lifted up from the outer circumferential surface of the rotating shaft into a noncontact state. This configuration prevents abrasion of and heat generation in the thin-plate seal pieces and the rotating shaft. The bottom surfaces of the thin-plate seal pieces refer to surfaces facing the rotating shaft, and the top surfaces thereof refer to surfaces opposite to the bottom surfaces.
Such a conventional shaft seal mechanism is disclosed, for example, in Patent Document 1 listed below.